The invention relates to a flat tube of a heat exchanger in heating installations or of a radiator of a motor vehicle with the features of the preamble of claim 1. Such a flat tube is known from the German Utility Model G 93 09 822.7, in particular FIGS. 6 to 7b. 
In the known flat tube, the dents of at least one flat side of the flat tube are arranged such that on the one hand a mutual holding stabilization of the flat sides against bursting pressure is effected and on the other hand a desired generation of turbulences is achieved.
For the generation of turbulences, the spacers have to be arranged relatively closely to one another. This, however, results in a relatively marked mutual blocking of the flow resulting in a maximum turbulence in direct proximity to the spacers and a relatively low degree of flow turbulences therebetween. The high turbulence in the proximity to the spacers leads to a relatively high degree of erosion.
A multiplicity of types of dented spacers soldered or brazed to one another in flat tubes folded from sheet metal are also known otherwise (e.g. GB-2 223 091 A and DE 15 01 537 A).
The object underlying the invention is to even out the generation of turbulences such that the danger of erosion is reduced at the same time maintaining a sufficient safety of the flat tube against bursting.
In a flat tube of a heat exchanger in heating installations or of radiator of a motor vehicle which is folded from a flat sheet metal of aluminum or an aluminum alloy and across the respective flow of which spacers of the flat sides of the flat tube are distributed, which are soldered or brazed to one another and designed as dents of the flat sides of the flat tube on one or both sides, this object is achieved by the characterized features there of.
Two alternative preferred arrangements of the spacers are possible here only arranged in a relatively low number. The spacers may be aligned centrally flushing longitudinally of the flow which is particularly convenient for rather narrow flows and the spacers are laterally staggered at opposite sides longitudinally of the flow which is for rather broad flows. Here, it is no longer necessary to distribute the spacers in a grid across the width of the respective flow as is done in the known flat tubes, but according to the former embodiment they can be optimally arranged fluidically even in only one line and according to the latter embodiment in two lines longitudinal of the flow one after the other and thus the risk of an erosion in particular at the side of the incoming flow can be further reduced. This is even more true if an embossment each is arranged preceding the spacer in the flow direction, so as to say as a bulwark.
In the special case of flat tubes of at least two flows, it is convenient with spacers being adjacent to the partition between the flows to surround the region not adjacent to the partition with a gross of embossments. In case of other spacers arranged at a distance to lateral partitions of an arbitrary number of flows, in particular also in case of one-flow flat tubes, the spacers can be surrounded all around by a group of embossments.
If the spacers are designed as elongated flow profiles, it is recommendable to intercalate at least one embossment between the spacers, but furthermore to arrange longitudinally of the flow profile at least in regions facing away from a partition between adjacent flows at least two embossments in the flow direction one after the other.
In general, a design having the embossments distributed in a point raster or the embossments are shaped like calotte shells has proved to be convenient for the arrangement and embodiment of the embossments.
The design of the spacers themselves is selected in the sense of the object of the invention to keep the erosion at the spacers as low as possible. In this respect, the oval central soldering or brazing joint itself only offers little resistance against erosion. In particular the funnel-shaped inflow leads to a flow deflection. This effect is favourably increased by the preferably provided dent, preferably in the funnel-shaped inflow region, but also in the funnel-shaped outflow region, due to the fact that the dents themselves take over the function of bulwarks.